Antenna structures having planar inverted F-antenna that surrounds an artificial magnetic conductor cell

ABSTRACT

Integrated antenna structures described herein include, as one example, a multi-layered printed circuit board (PCB), including an artificial magnetic conductor (AMC) cell that includes a backing metal layer defining a first inner layer of the multi-layered PCB and an AMC metal layer defining a second inner layer of the multi-layered PCB. The metal layer defining the second inner layer is separated from at least one edge of the multi-layered PCB, and a planar inverted F antenna (PIFA) surrounds the AMC cell. The AMC metal layer is configured to reflect energy radiated by the PIFA. In some embodiments, the energy radiated by the PIFA includes radio frequency waves that can be used by a receiver to power or charge an electronic device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/586,134, filed on Dec. 30, 2014, entitled “Integrated Miniature PIFAWith Artificial Magnetic Conductor Metamaterials,” which is acontinuation-in-part of U.S. patent application Ser. No. 14/336,971,filed on Jul. 21, 2014, entitled “Integrated Miniature PIFA withArtificial Magnetic Conductor Metamaterials,” (U.S. Pat. No. 9,871,301),each of which is herein fully incorporated by reference in itsrespective entirety

This application is related to U.S. Non-Provisional patent applicationSer. No. 14/583,625, filed Dec. 27, 2014, entitled “Receivers forWireless Power Transmission,” U.S. Non-Provisional patent applicationSer. No. 14/583,630, filed Dec. 27, 2014, entitled “Methodology forPocket-Forming,” U.S. Non-Provisional patent application Ser. No.14/583,634, filed Dec. 27, 2014, entitled “Transmitters for WirelessPower Transmission,” U.S. Non-Provisional patent application Ser. No.14/583,640, filed Dec. 27, 2014, entitled “Methodology for MultiplePocket-Forming,” U.S. Non-Provisional patent application Ser. No.14/583,641, filed Dec. 27, 2014, entitled “Wireless Power Transmissionwith Selective Range,” U.S. Non-Provisional patent application Ser. No.14/583,643, filed Dec. 27, 2014, entitled “Method for 3 DimensionalPocket-Forming,” all of which are incorporated herein by reference intheir entirety.

BACKGROUND

Field of the Disclosure

The present disclosure relates in general to antennas, and morespecifically, to compact and directional planar inverted-F antennas(PIFAs) integrated in artificial magnetic conductor metamaterials whichmay be used for wireless power transmission.

Background

Wireless power transmission may include a transmitter for forming anddirecting radio frequency (RF) waves towards a receiver which mayconvert RF waves into usable power for charging or powering anelectronic device. The receiver may be integrated in the electronicdevice (e.g., a smartphone, a tablet) or may be in the form of casesthat may be operatively coupled with the electronic device for suitablecharging or powering. The transmitter may be an antenna array that mayinclude N antennas which may be directional.

The antenna array may be controlled by computer hardware and software inorder to broadcast a wireless signal towards the receiver. Amplitude andphase among other properties of the transmitted RF waves may be tuned bythe computer hardware and software to form constructive and destructiveinterference patterns generating pockets of energy in a 3-dimensionalshape from the constructive patterns, and null spaces from thedestructive patterns to aim the pockets of energy to specific receivers.

The number of antennas in the antenna array may vary in relation withthe desired power range and transmission capability of the transmitter.The more antennas the wider the range and higher the power transmissionpotential available at the transmitter. More antennas may additionallyenable the transmitter to target more receivers at once. Directionalantenna designs that can be integrated in transmitters may include Yagi,log-periodic, corner reflectors, and parabolic antennas, among others.

However, size may be one important factor that may impact the number ofantennas that can be integrated in the antenna array for thetransmitter. Designers often look for the optimal combination of sizeand performance in the antennas integrated in the transmitter, where theperformance is usually hampered when size is reduced.

Planar inverter F antennas (PIFA) may be fabricated in small formfactors that may allow for dense antenna arrays. However, PIFA antennas'radiation pattern is commonly omnidirectional, which might mean than atransmitter including an antenna array of PIFA antennas may wastetransmitted power. Additionally the omnidirectional radiation patternsmay hinder the transmitter ability to focus the transmitted RF waves tospecific receivers.

For the foregoing reasons, there is a need for a directional antennathat may enable for the construction of tightly packaged antenna arraysthat may render reasonable small sizes of antenna arrays while keeping asuitable performance.

SUMMARY

Various embodiments of a PIFA integrated with artificial magneticconductors (AMC) metamaterials described herein may include a PIFA, anAMC metal layer, and a backing metal conductor formed on a multi-layerprinted circuit board (PCB).

In one exemplary embodiment of the present disclosure, a folded groundplanar array inverted-F (PIFA) is disclosed. The folded ground PIFA mayinclude an antenna element with two or more slots formed over the toplayer of a PCB, where these antenna slots may be designed for reducingthe area of the antenna while keeping a suitable impedance bandwidth.These PIFA configurations may also include a ground element formed onthe bottom layer of the PCB and operatively coupled with the antennaelement through ground and signal vias. The ground element may include aslot designed for reducing the area of the ground while increasing theradiation efficiency of the PIFA system. The missing central ground areadoes not affect antenna operation except possibly in de-tuning theimpedance bandwidth, which can be adjusted by the antenna elementitself.

In one embodiment, a PIFA configuration may include a folded groundformed over the empty space of a PCB top layer, without interfering withthe operation of an antenna element which may be also formed over thePCB top layer. This folded ground may be operatively connected with aground element on the PCB bottom layer through folded ground vias.Folded ground may allow the reduction in the system area whilemaintaining an omnidirectional radiation pattern and a suitableperformance in terms of impedance bandwidth and radiation efficiency.

In another embodiment of the present disclosure, an AMC unit cell mayinclude an AMC metal layer and a backing metal layer. The AMC metallayer and the backing metal layer may be formed in the inner layers of amulti-layer PCB. In some embodiments, the edges of the AMC metal layermay be close to the edges of the AMC unit cell but not coincident.

In one embodiment, the AMC metal layer of an AMC unit cell may exhibit asquare θ ring shape, while in other embodiments, the AMC metal layer mayexhibit a square ring shape. Yet in other embodiments, the AMC metallayer may be of any shape and size. The shape and dimensions of the AMCunit cell may determine the frequency tuning of AMC unit cellfunctionality.

In one embodiment of the present disclosure, a first AMC metamaterialembodiment may be formed with 5×5 array of AMC unit cells, where eachAMC unit cell may include an AMC metal layer that may exhibit a square 0ring shape and a backing metal layer. The first AMC metamaterial may beformed over a large multi-layer and monolithic PCB that may fit aplurality of AMC unit cells. According to some aspects of thisembodiment, the 5×5 array of AMC unit cells may exhibit the propertiesof an AMC metamaterial. The AMC metamaterial may be tuned to a resonantfrequency which may be designed to be the low-band edge of a desiredfrequency band.

In another embodiment, a second AMC metamaterial embodiment may beformed with 6×6 array of AMC unit cells, where each AMC unit cell mayinclude an AMC metal layer which may exhibit a square ring shape, and abacking metal layer. The second AMC metamaterial may be formed over alarge multi-layer and monolithic PCB that may fit a plurality of AMCunit cells. According to some aspects of this embodiment, the 5×5 arrayof AMC unit cells may exhibit the properties of an AMC metamaterial. TheAMC metamaterial may be tuned to a resonant frequency which may bedesigned to be the low-band edge of a desired frequency band.

One exemplary embodiment of the present disclosure may include theintegration of a PIFA with a first AMC metamaterial to form a firstintegrated antenna structure. In the first integrated antenna structure,the AMC metal layer and backing conductor of the first metamaterial maybe formed on the inner layers of a four layer PCB, while antennaelements and ground elements of the PIFA may be formed on top and bottomlayers of a PCB, respectively. In some embodiments, a hole may be madein the metal backing conductor to allow signal and ground vias from PIFAto traverse the backing metal layer without contact, while the foldedground vias in PIFA may be short-circuited with the backing metal layer.

Another exemplary embodiment of the present disclosure may include theintegration of a PIFA with a second AMC metamaterial to form a secondintegrated antenna structure. In the second integrated antennastructure, the AMC metal layer and backing conductor of the secondmetamaterial embodiment may be formed on the inner layers of a fourlayer PCB, while antenna elements and ground elements of the PIFA may beformed on top and bottom layers of a PCB, respectively. In someembodiments, a hole may be made in the metal backing conductor to allowsignal and ground vias from PIFA to traverse the backing metal layerwithout contact, while the folded ground vias in PIFA may beshort-circuited with the backing metal layer.

In yet other embodiments, where the PIFA has no folded ground, foldedground vias of PIFA may still be formed in the PCB and beshort-circuited with the backing metal layer.

According to some aspects of the present disclosure the integratedantenna structures may exhibit a directional radiator pattern.

The AMC metamaterial in the integrated antenna structures may operate asan artificial magnetic reflector that may send upwards all energyradiated by the PIFA, thus achieving a directional radiation pattern.More specifically, the integrated antenna structures may exhibit adirectional broadside pattern that may be about twice of that of theomnidirectional radiation pattern exhibited by PIFA alone. In addition,the relatively small system area of the integrated antenna structuresmay enable the fabrication of compact directional antenna arrays thatmay be suitable for small system area transmitters. The relatively smallsystem area of the integrated antenna structures described herein may beconsiderable smaller than those of traditional directional antennas.

Numerous other aspects, features and benefits of the present disclosuremay be made apparent from the following detailed description takentogether with the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure can be better understood by referring to thefollowing figures. The components in the figures are not necessarily toscale, emphasis instead being placed upon illustrating the principles ofthe disclosure. In the figures, reference numerals designatecorresponding parts throughout the different views.

FIG. 1A shows an isometric view of a planar inverted-F antennaintegrated in a printed circuit board, according to an embodiment.

FIG. 1B illustrates a side view of planar inverted-F antenna integratedin a printed circuit board, according to an embodiment.

FIG. 2A shows an omnidirectional isometric radiation pattern of thePIFA, according to an embodiment.

FIG. 2B depicts the return loss of the PIFA when fed by a 50-Ohm port,according to an embodiment.

FIG. 3 illustrates a side view of an exemplary AMC unit cell of an AMCmetamaterial, according to an embodiment.

FIG. 4A illustrates an isometric view of a unit cell of an AMCmetamaterial that may include AMC metal layers resembling a square θring, according to an embodiment.

FIG. 4B illustrates a top view of the AMC unit cell of an AMCmetamaterial, according to an embodiment.

FIG. 5 illustrates an isometric view a 5×5 array AMC unit cells of anAMC metamaterial that may include AMC metal layers that may resemble a θsquare ring, according to an embodiment.

FIG. 6 illustrates the complex reflection coefficient of an incidentplane wave at the surface of an AMC metamaterial that may include AMCmetal layers that may resemble a square θ ring, according to anembodiment.

FIG. 7A shows an isometric view of an AMC unit cell of a metamaterialthat may include AMC metal layers resembling a square ring, according toan embodiment.

FIG. 7B illustrates a top view of the AMC unit cell of an AMCmetamaterial, according to an embodiment.

FIG. 8 illustrates an isometric view of a 6×6 array unit cells of an AMCmetamaterial that may include AMC metal layers resembling a square ring,according to an embodiment.

FIG. 9 shows the complex reflection coefficient of an incident planewave at the surface of an AMC metamaterial that may include AMC metallayers that may resemble a square ring, according to an embodiment.

FIG. 10 illustrates an isometric view of an exemplary integration of aPIFA with AMC metamaterial that may include an AMC metal layer that mayresemble a θ square ring, according to an embodiment.

FIG. 11A illustrates a top view of an exemplary integration of a PIFAwith AMC metamaterial that may include an AMC metal layer that mayresemble a 0 square ring, according to an embodiment.

FIG. 11B illustrates a side view of an exemplary integration of a PIFAwith AMC metamaterial that may include an AMC metal layer that mayresemble a 0 square ring, according to an embodiment.

FIG. 12A illustrates the impedance bandwidth response of an exemplaryintegration of a PIFA with AMC metamaterial that may include an AMCmetal layer that may resemble a square θ ring, according to anembodiment.

FIG. 12B illustrates the radiation pattern of an exemplary integrationof a PTFA with AMC metamaterial that may include an AMC metal layer thatmay resemble a square θ ring, according to an embodiment

FIG. 13 illustrates an isometric view of an exemplary integration of aPIFA with AMC metamaterial that may include an AMC metal layer that mayresemble a square ring, according to an embodiment.

FIG. 14A illustrates a top view of an exemplary integration of a PIFAwith AMC metamaterial that may include an AMC metal layer that mayresemble a square ring, according to an embodiment.

FIG. 14B illustrates a side view of an exemplary integration of a PIFAwith AMC metamaterial that may include an AMC metal layer that mayresemble a square ring, according to an embodiment

FIG. 15A illustrates the impedance bandwidth response of an exemplaryintegration of a PTFA with AMC metamaterial that may include an AMCmetal layer that may resemble a square ring, according to an embodiment.

FIG. 15B illustrates the radiation pattern of all exemplary integrationof a PTFA with AMC metamaterial that may include an AMC metal layer thatmay resemble a square ring, according to an embodiment

DETAILED DESCRIPTION

The present disclosure is here described in detail with reference toembodiments illustrated in the drawings, which form a part here. Otherembodiments may be used and/or other changes may be made withoutdeparting from the spirit or scope of the present disclosure. Theillustrative embodiments described in the detailed description are notmeant to be limiting of the subject matter presented here.

Definitions

“Pocket-forming” may refer to generating two or more RF waves whichconverge in 3-d space, forming controlled constructive and destructiveinterference patterns.

“Pockets of energy” may refer to areas or regions of space where energyor power may accumulate in the form of constructive interferencepatterns of RF waves.

“Null-space” may refer to areas or regions of space where pockets ofenergy do not form because of destructive interference patterns of RFwaves.

“Transmitter” may refer to a device, including a chip which may generatetwo or more RF signals, at least one RF signal being phase shifted andgain adjusted with respect to other RF signals, substantially all ofwhich pass through one or more RF antenna such that focused RF signalsare directed to a target.

“Receiver” may refer to a device which may include at least one antenna,at least one rectifying circuit and at least one power converter forpowering or charging an electronic device using RF waves.

“Adaptive pocket-forming” may refer to dynamically adjustingpocket-forming to regulate power on one or more targeted receivers.

“Metamaterial” a synthetic composite material with a structure such thatit exhibits properties not usually found in natural materials. Forexample naturally occurring materials normally exhibit a positiverefraction index for electromagnetic waves. However, fabricatedmetamaterials may exhibit a negative refractive index.

“AMC Metamaterial” may refer to an artificial magnetic conductor (AMC)metamaterial that exhibits functionality so that the complex reflectioncoefficient (S) of a normally incident plane wave, at the material'ssurface, be S≈1. This makes the total electric field, tangential to thematerial's surface (which is the sum of the incident and reflectedelectric fields) to be twice as large as the incident field. Incontrast, on common metal surfaces (electric conductors), the totalfield under these conditions is null. More generally, the materialexhibits sufficient AMC bandwidth defined as the frequency band wherethe real part of the complex reflection coefficient is greater than zero(Re {S}≥0).

“AMC Unit cell” may refer to the parts from which an AMC metamaterialmay be composed.

Description of the Drawings

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings, whichmay not be to scale or to proportion, similar symbols typically identifysimilar components, unless context dictates otherwise. The illustrativeembodiments described in the detailed description, drawings and claims,are not meant to be limiting. Other embodiments may be used and/or otherchanges may be made without departing from the spirit or scope of thepresent disclosure.

The present disclosure relates to antennas, and more specifically, tocompact and directional planar inverted-F antennas (PIFAs) withmetamaterials that may be integrated in antenna arrays for wirelesspower transmission. An antenna design with small system area may beintegrated in artificial magnetic conductor (AMC) metamaterial. The AMCmetamaterial may provide the antenna with directionality that may enablethe fabrication of compact directional antenna arrays.

Miniature PIFA Architecture

FIGS. 1A and 1B illustrate a PIFA 100 with a folded ground 102 that maybe formed over the top and bottom layers of a multi-layer printedcircuit board (PCB). FIG. 1A shows of an isometric view of PIFA 100according to embodiments of the present disclosure. FIG. 1B shows a sideview of PIFA 100.

FIG. 1A illustrates an isometric view of PIFA 100 which may be designedto be as small as possible while maintaining suitable performance forwireless power transmission, and it may be formed in a multi-layerprinted circuit board (PCB 104) for achieving a monolithic form. In oneembodiment, PIFA 100 may be formed on its own PCB 104 which may beconnected to the PCB of an electronic device or a transmitter. Inanother embodiment, several PIFAs 100 may be formed on a largemulti-layer PCB that may be part of a transmitter.

PIFA 100 may include an antenna element 106 formed over the top layer ofPCB 104, and a ground element 108 formed over the bottom layer of PCB104. Both PCB layers may be made of suitable metals such as copper ofsmall metal thickness relative to the total PCB 104 thickness.

Antenna element 106 may include two antenna slots 110 designed forreducing the area of antenna element 106 while maintaining a suitablebandwidth operation. More antenna slots 110 may be introduced on antennaelement 106 for even further area reduction if necessary, according toapplication.

Similarly to antenna element 106, ground element 108 may include aground slot 120 whose main purpose may be reducing the area of theground element 108 while reducing losses and increasing radiationefficiency.

PIFA 100 may also include a signal via 112, a ground via 114, and a RFport 116 for electrical connection purposes. In one embodiment, asemi-rigid 50 Ohm coax cable can be connected to RF port 116 forprototype measurements. For integration purposes, PIFA 100 may be fedthrough RF port 116 by a transmission line integrated in a larger PCB.

Folded ground 102 on PIFA 100 may be formed over an empty region of PCB104 top layer without interfering with the performance of antennaclement 106. Folded ground 102 may be raised over the top layer of PCB104 and may be connected to ground element 108 through folded groundvias 118 which may not significantly affect the performance of PIFA 100.Folded ground 102 may act as an extension of ground element 108.

According to some aspects of this embodiment, folded ground 102 mayallow to reduce the dimensions of PIFA 100. PIFA 100 dimensions in thex-axis, y-axis, and z-axis may be about 10 mm, 30 mm, and 24 mmrespectively, for a system area of about 30 mm² and a system volume ofabout 72 mm³.

FIG. 1B illustrates a side view of PIFA 100 where folded ground 102 andantenna element 106 may be formed on top of PCB 104. Ground element 108may be formed on the bottom of PCB 104. Folded ground vias 118, signalvia 112, and ground via 114 are also shown in FIG. 1B.

FIGS. 2A and 2B show an omnidirectional isometric radiation pattern 200of PIFA 100 (as oriented in FIGS. 1A and 1B). This omnidirectionalradiation pattern in FIG. 2A may be similar to radiation patternsexhibited in dipole antennas, thereby allowing flexible placement orintegration of PIFA into larger form factors systems or PCBs. In oneembodiment, PTFA 100 may exhibit a maximum gain of about +0.49 dBi at5.8 GHz.

FIG. 2B illustrates the return loss of PIFA 100 when fed by a 50-Ohmport. As seen from probes m1 and m2, PIFA 100 may exhibit an impedancebandwidth of about 210 MHz at −10 dB, where this bandwidth may providesufficient margins for possible detuning upon integration of PIFA intoan electronic device or a larger PCB. Radiation efficiency of PIFA maybe around 80% at about 5.8 GHz.

Although PIFA 100 may exhibit suitable characteristics for wirelesspower transmission, it may be an object of the following embodiments toprovide integrated antenna structures with a similar monolithic PCB formfactor, and performance in terms of bandwidth and radiation efficiency,but with a directional radiation pattern suitable for transmission offocused RF waves.

AMC Unit Cells and AMC Unit Cell Arrays

FIG. 3 illustrates a side view of an exemplary embodiment of an AMC unitcell 300 of an AMC metamaterial in which PIFA 100 may be integrated. AMCUnit cell 300 may include an AMC metal layer 302, a backing metal layer304. AMC Unit cell 300 may be formed in a multi-layer printed circuitboard (PCB 306) for achieving a monolithic form. Edge 308 of AMC unitcell 300 may be close to AMC metal layer 302 but not coincident to edge308 of AMC metal layer 302. In one embodiment, several AMC unit cells300 of an AMC metamaterial may be formed on a larger multi-layer PCB.

A large variety of elements design in an AMC unit cell 300 may berealized on a multi-layer PCB 306 that may fulfill the requiredfunctionality of an AMC metamaterial. Arrays of AMC unit cells 300 mayadditionally be integrated with PIFAs; two exemplary designs areillustrated and listed in the following description.

First AMC Unit Cell Exemplary Embodiment

FIGS. 4A and 4B illustrate an exemplary design of an AMC unit cell 400according to an embodiment. FIG. 4A illustrates an isometric view of AMCunit cell 400, while FIG. 4B illustrates a top-view of AMC unit cell400.

FIG. 4A illustrates an isometric view of AMC unit cell 400 that mayinclude an AMC metal layer 402 and backing metal layer 304. AMC metallayer 402 may exhibit a square 0 ring shape, and may be formed on atleast one inner layer of a multi-layer PCB 404. Backing metal layer 304may be formed on another layer of PCB 404.

Dimensions of AMC unit cell 400 illustrated in FIG. 4A may be about 0.06mm, 0.887 mm, and 1.453 mm for t, s, and g, respectively.

A side view of AMC unit cell 400 is illustrated in FIG. 4B. Distance (d)between outer edge of AMC unit cell 400 and outer edge of AMC metallayer 402 may be about 0.0425 mm. Dimensions of AMC metal layer 402illustrated in FIG. 4B may be about 0.276 mm, 0.135 mm, and 3.581 mm forb, c, and a, respectively.

These dimensions as well as the shape exhibited by AMC metal layer 402may determine the frequency tuning and bandwidth of AMC unit cell 400functionality.

First AMC Metamaterial Exemplary Embodiment

FIG. 5 illustrates an exemplary embodiment of a first AMC metamaterial500. AMC metamaterial 500 may exhibit a configuration of 5×5 array ofAMC unit cells 400. AMC unit cells 400 in AMC metamaterial 500 mayinclude AMC metal layer 402 and backing metal layer 304. AMCmetamaterial 500 may be formed over a large monolithic multi-layer PCB502 to fit a plurality of AMC unit cells 400. According to some aspectsof this embodiment, AMC metamaterial 500 may exhibit the properties ofan AMC metamaterial.

FIG. 6 illustrates the complex reflection coefficient graph 600 of AMCmetamaterial 500 computed on its top surface, under normal plane waveincidence on a laterally infinite 2-dimensional artificial crystal. Thereal part of the reflection coefficient may have the property Re {S}≥0in the frequency range of about 5.15 to about 6.05 GHz, for an estimatedbandwidth of about 900 MHz. AMC metamaterial 500 may be tuned to aresonant frequency of about 5.65 GHz which may be designed to be thelow-band edge of a desired impedance-matched frequency band. Thecorresponding value of the complex reflection coefficient for AMCmetamaterial 500 at a resonant frequency of 5.65 GHz may be S=0.9+j0.

In one embodiment, AMC unit cell 400 dimensions may be about0.068×0.068×0.046λ³, where λ may be the wavelength at the resonantfrequency of the AMC unit cell 400. These dimensions exhibited by AMCunit cell 400 may be suitable for integration with small PIFAs such asPIFA 100. A plurality of AMC unit cells 400 may be required to recreatea metamaterial that may impose AMC functionality to an antenna such asPIFA 100.

Second AMC Unit Cell Exemplary Design

FIGS. 7A and 7B illustrate an exemplary design of an AMC unit cell 700,according to an embodiment. FIG. 7A illustrates an isometric view of AMCunit cell 700, while FIG. 7B illustrates a top-view of AMC unit cell700.

FIG. 7A illustrates an isometric view of an AMC unit cell 700 that mayinclude all AMC metal layer 702 and backing metal layer 304. AMC metallayer 702 may exhibit a square ring shape and may be formed on one ofthe inner layers of a multi-layer PCB 704. Backing metal layer 304 maybe formed on another layer of PCB 704.

Dimensions of AMC unit cell 700 illustrated in FIG. 7A may be about 0.06mm, 0.887 mm, and 1.453 for t, s, and g, respectively.

A top view of AMC unit cell 700 is illustrated in FIG. 7B where distance(d) between outer edge of AMC unit cell 700 and outer edge of AMC metallayer 702 may be about 0.04 mm. Additionally, the dimensions of AMCmetal layer 702 may be about 0.23 mm, and 3 0 mm for b, and a,respectively.

Second AMC Metamaterial Exemplary Embodiment

FIG. 8 illustrates an exemplary embodiment of a second AMC metamaterial800. AMC metamaterial 800 may exhibit a configuration of 6×6 array ofAMC unit cells 700. AMC unit cells 700 in AMC metamaterial 800 mayinclude AMC metal layer 702 and backing metal layer 304. AMCmetamaterial 800 may be formed over a large monolithic multi-layer PCB802 to fit a plurality of AMC unit cells 700. According to some aspectsof this embodiment, AMC metamaterial 800 may exhibit the properties ofan AMC metamaterial.

FIG. 9 illustrates the complex reflection coefficient response 900 ofAMC metamaterial 800 computed on its top surface, under normal planewave incidence on a laterally infinite 2-dimensional artificial crystal.The real part of the reflection coefficient may have the property Re{S}≥0 in the frequency range of about 5.25 to about 6.1 GHz, for anestimated bandwidth of about 850 MHz. AMC metamaterial 800 may be tunedto a resonant frequency of about 5.7 GHz which may be designed to be thelow-band edge of a desired impedance-matched frequency band. Thecorresponding value of the complex reflection coefficient for AMCmetamaterial 800 at a resonant frequency of 5.7 GHz may be S=0.9+j0.

In one embodiment, AMC unit cell 700 dimensions may be about0.057×0.057×0.046λ³, where λ may be the wavelength at the resonantfrequency of the AMC unit cell 700. These dimensions exhibited by AMCunit cell 700 may be suitable for integration with small PIFAs such asPIFA 100. A plurality of AMC unit cells 700 may be required to recreatea metamaterial that may impose AMC functionality to an antenna such asPIFA 100.

Integrated Antenna Structures

PIFA and AMC metamaterial integration may be realized on a multi-layerPCB that may fulfill the required functionality of a directionalantenna; two exemplary embodiments of integrated antenna structures areillustrated and described below, where these integrated antennastructures may be part of a transmitter device configured for sendingfocused RF waves towards a receiver for wireless charging or powering.

Integrated Antenna Structure Including PIFA+First AMC Metamaterial

FIG. 10 illustrates an isometric view of an exemplary integrated antennastructure 1000 that may include first AMC metamaterial 500 integratedwith PIFA 100.

Integrated antenna structure 1000 may include a monolithic four layerPCB 1002 that may be used as a substrate to suitably integrate AMCmetamaterial 500 with PIFA 100. For example, antenna element 106 andfolded ground 102 of PIFA 100 may be formed on the top layer of PCB1002; AMC metal layer 402 of AMC metamaterial 500 may be formed in oneof the inner layers of PCB 1002; Backing metal layer 304 of AMCmetamaterial 500 may be formed on the other available inner layer of PCB1002; and ground element 108 of PTFA 100 may be formed on the bottomlayer of PCB 1002.

A hole 1004 may be formed in backing metal layer 304 for allowing signalvia 112 and ground via 114 to pass through backing metal layer 304without electrically shortening it. As a result, ground element 108 ofPIFA 100 shorted with backing metal layer 304 may become the primaryground of the integrated antenna structure 1000. At the opposite ends ofthis primary ground, folded ground vias 118 may short-circuit backingmetal layer 304 at a crossing point. In another embodiment where PIFA100 has no folded ground 102, folded ground vias 118 may be also formedto electrically short backing metal layer 304 and ground element 108.

In other embodiments, PIFA 100 may have different dimensions andconfigurations than those described in FIGS. 1A and 1B.

FIGS. 11A and 11B illustrate top and side views of integrated antennastructure 1000. In some embodiments, as illustrated in FIG. 11A, PIFA100 may occupy about three AMC unit cells 400 of the AMC metamaterial500 formed on PCB 1002. In some embodiments as illustrated in FIG. 11A,integrated antenna structure 1000 may include dimensions of about 18 mmand 18 mm form and n respectively, for a system area of about 324 mm².

FIG. 11B shows a side view of integrated antenna structure 1000 where itmay be noticed how the AMC metamaterial 500 is integrated with PIFA 100.As shown in FIG. 11B, antenna element 106 and folded ground 102 may beformed on top side of PCB 1002, while ground element 108 may be formedon the bottom side of PCB 1002. Backing metal layer 304 and AMC metallayer 402 may be formed in the inner layers of PCB 1002, between antennaelement 106 and ground element 108. Folded ground vias 118, signal via112, and ground via 114 are also illustrated in FIG. 11B according toembodiments described herein. Thickness h of integrated antennastructure 1000 may be about 2.4 mm.

Overall dimensions for integrated antenna structure 1000 may varyaccording to the dimensions used for the AMC unit cells 400 and PIFA100, as well as the desired application.

FIGS. 12A and 12B illustrate the return loss and radiation pattern 1200of exemplary integrated antenna structure 1000 when fed by a 50-Ohmport. As shown in FIG. 12A, integrated antenna structure 1000 mayexhibit an impedance bandwidth of about 160 MHz at −10 dB, where thisbandwidth may provide sufficient margins for possible detuning uponintegration of the exemplary integrated antenna structure 1000 into anelectronic device or a larger PCB. Radiation efficiency of integratedantenna structure 1000 may be of about 72% at 5.8 GHz. The 8% point-dropfrom the efficiency of PIFA 100 may be due to the integration of the AMCmetamaterial 500, specifically the addition of the metallization layers,AMC metal layer 302 and backing metal layer 304.

FIG. 12B illustrates the radiation pattern of integrated antennastructure 1000, where the maximum gain may be of about 2.2 dBi at 5.8GHz. Integrated antenna structure 1000 may exhibit a directionalradiation pattern, more specifically, a directional broadside patternthat may be about twice of that of the omnidirectional radiation patternexhibited by PIFA 100 in FIGS. 2A and 2B. In this way, by integratingthe AMC metamaterial 500 with PIFA 100 in the integrated antennastructure 1000, the omnidirectional pattern of PIFA 100 may be changedto a directional pattern as exhibited in FIG. 12B, where the AMCmetamaterial 500 may operate as an artificial magnetic reflector,sending all the energy upwards. Still, the overall dimensions ofintegrated antenna structure 1000 may be about 0.345×0.345×0.05λ³ whichmay significantly smaller compared to conventional directional antennassuch as a half-wave conductor-backed dipole. For example, a half-wavecenter-fed linear dipole with a quarter-wave backing metal reflector mayneed a system size of at least 0.5×0.5×0.25λ³ to achieve a similarperformance of integrated antenna structure 1000.

Integrated Antenna Structure Including PIFA+Second AMC MetamaterialEmbodiment

FIG. 13 illustrates an isometric view of an exemplary integrated antennastructure 1300 that may include second AMC metamaterial 800 integratedwith PIFA 100.

Integrated antenna structure 1300 may include a monolithic four layerPCB 1302 that may be used as a substrate to suitably integrate AMCmetamaterial 800 with PIFA 100. For example, antenna element 106 andfolded ground 102 of PIFA 100 may be formed on the top layer of PCB1302; AMC metal layer 702 of AMC metamaterial 800 may be formed in oneof the inner layers of PCB 1302; Backing metal layer 304 of AMCmetamaterial 800 may be formed on the other available inner layer of PCB1302; and ground element 108 of PIFA 100 may be formed on the bottomlayer of PCB 1302.

A hole 1304 may be formed in backing metal layer 304 for allowing signalvia 112 and ground via 114 to pass through backing metal layer 304without electrically shortening it. As a result, ground element 108 ofPIFA 100 shorted with backing metal layer 304 may become the primaryground of the integrated antenna structure 1300. At the opposite ends ofthis primary ground, folded ground vias 118 may short-circuit backingmetal layer 304 at a crossing point. In another embodiment where PIFA100 has no folded ground 102, folded ground vias 118 may be also formedto electrically short backing metal layer 304 and ground element 108.

In other embodiments, PIFA 100 may have different dimensions andconfigurations than those described in FIGS. 1A and 1B.

FIGS. 14A and 14B illustrate top and side views of integrated antennastructure 1300. In some embodiments, as illustrated in FIG. 14A, PIFA100 may occupy about eight AMC unit cells 700 of the AMC metamaterial800 formed on PCB 1302. In some embodiments as illustrated in FIG. 14A,integrated antenna structure 1300 may include dimensions of about 18 mmand 18 mm form and n respectively, for a system area of about 324 mm².

FIG. 14B shows a side view of integrated antenna structure 1300 where itmay be noticed how the AMC metamaterial 800 is integrated with PIFA 100.As shown in FIG. 14B, antenna element 106 and folded ground 102 may beformed on top side of PCB 1302, while ground element 108 may be formedon the bottom side of PCB 1302. Backing metal layer 304 and AMC metallayer 702 may be formed in the inner layers of PCB 1302, between antennaelement 106 and ground element 108. Folded ground vias 118, signal via112, and ground via 114 are also illustrated in FIG. 14B according toembodiments described herein. Thickness h of integrated antennastructure 1300 may be about 2.4 mm.

Overall dimensions for integrated antenna structure 1300 may varyaccording to the dimensions used for the AMC unit cells 700 and PIFA100, as well as the desired application.

FIGS. 15A and 15B illustrate the return loss and radiation pattern 1500of exemplary integrated antenna structure 1300 when fed by a 50-Ohmport. As shown in FIG. 15A, integrated antenna structure 1300 mayexhibit an impedance bandwidth of about 160 MHz at −10 dB, where thisbandwidth may provide sufficient margins for possible detuning uponintegration of the exemplary integrated antenna structure 1300 into anelectronic device or a larger PCB. Radiation efficiency of integratedantenna structure 1300 may be of about 67% at 5.8 GHz. The 13%point-drop from the efficiency of PIFA 100 may be due to the integrationof the AMC metamaterial 800, specifically the addition of themetallization layers, AMC metal layer 702 and backing metal layer 304,configured in a larger 6×6 array compared to the 5×5 array configured inAMC metamaterial 500, hence the larger amount of AMC metallization andradiation efficiency degradation.

FIG. 15B illustrates the radiation pattern of integrated antennastructure 1300, where the maximum gain may be of about 2.0 dBi at 5.8GHz. Integrated antenna structure 1300 may exhibit a directionalradiation pattern, more specifically a directional broadside patternthat may be about twice of that of the omnidirectional radiation patternexhibited by PIFA 100 in FIGS. 2A and 2B. In this way, by integratingthe AMC metamaterial 800 with PIFA 100 in the integrated antennastructure 1300, the omnidirectional pattern of PIFA 100 may be changedto a directional pattern as exhibited in FIG. 15B, where the AMCmetamaterial 800 may operate as an artificial magnetic reflector,sending all the energy upwards. Still, the overall dimensions ofintegrated antenna structure 1300 may be about 0.345×0.345×0.05λ³ whichmay significantly smaller compared to conventional directional antennassuch as a half-wave conductor-backed dipole. For example, a half-wavecenter-fed linear dipole with a quarter-wave backing metal reflector mayneed a system size of at least 0.5×0.5×0.25 to achieve a similarperformance of integrated antenna structure 1300.

The embodiments of integrated antenna structures 1000, 1300 featuringthe integration of first AMC metamaterial 500 and second AMCmetamaterial 800 with PIFA 100 may suggest that as long as the twometamaterials may exhibit a similar response as shown in FIG. 6 and FIG.9, the integration of PIFAs with metamaterials described herein may berobust and may lead to similar results as shown in FIGS. 12A and 12B andFIGS. 15A and 15B.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

What is claimed is:
 1. An antenna structure comprising: a multi-layeredprinted circuit board (PCB), comprising an artificial magnetic conductor(AMC) cell that includes (i) a backing metal layer defining a firstinner layer of the multi-layered PCB and (ii) an AMC metal layerdefining a second inner layer of the multi-layered PCB, wherein themetal layer defining the second inner layer is separated from at leastone edge of the multi-layered PCB; and a planar inverted F antenna(PIFA) surrounding the AMC cell, wherein the AMC metal layer isconfigured to reflect energy radiated by the PIFA.
 2. The antennastructure of claim 1, wherein the AMC metal layer is separated from alledges of the multi-layered PCB.
 3. The antenna structure of claim 1,wherein the AMC metal layer has a square shape.
 4. The antenna structureof claim 3, wherein the square shape includes a metal divider thatdefines at least one inner rectangle.
 5. The antenna structure of claim4, wherein the metal divider defines at least two inner rectangles, eachof the two inner rectangles have a same set of dimensions, and the sameset of dimensions determines the frequency tuning and bandwidth of theAMC cell.
 6. The antenna structure of claim 1, wherein the AMC metallayer is configured to reflect energy radiated by the PIFA to produce adirectional radiation pattern.
 7. The antenna structure of claim 1,wherein the AMC metal layer comprises a metamaterial.
 8. The antennastructure of claim 1, wherein: the PIFA further comprises an antennaelement disposed over a part of a top portion of the multi-layered PCBand a ground element disposed over a part of a bottom portion of themulti-layered PCB, and the antenna element is coupled to the groundelement and a different part of the bottom portion of the multi-layeredPCB through a first ground via and a signal via, respectively, and theantenna structure further includes a folded ground formed over adifferent part of the top portion of the multi-layered PCB, and thefolded ground is coupled to the ground element through a second groundvia.
 9. The antenna structure of claim 8, wherein the ground elementcomprises a ground slot and the antenna element comprises an antennaslot.
 10. The antenna structure of claim 8, wherein the top and bottomportions of the multi-layered printed circuit board PCB comprise aconductive metal.
 11. The antenna structure of claim 1, wherein atransmitter coupled to the PIFA is configured to provide a signal forradiation by the PIFA.
 12. The antenna structure of claim 11, whereinthe transmitter comprises a processing apparatus for adjusting at leastone of a phase of the signal and a magnitude of the signal.
 13. Theantenna structure of claim 1, wherein the energy radiated by the PIFAincludes radio frequency waves.
 14. The antenna structure of claim 13,wherein the radio frequency waves are used by a receiver to power orcharge an electronic device.
 15. An apparatus for providing3-dimensional pockets of energy through pocket-forming, the apparatuscomprising: a multi-layered printed circuit board (PCB), comprising aplurality of artificial magnetic conductor (AMC) cells, wherein each ofthe AMC cells comprises a backing metal layer and an AMC metal layerdefining inner layers of the multi-layered PCB and is separated from atleast one edge of the multi-layered PCB, wherein each of the AMC layersis configured to reflect energy independently as radiated by each of aplurality of planar inverted F antennas (PIFAs) to enable pocket-formingof energy, wherein each of the PIFAs surrounds at least one AMC cell ofthe plurality of the AMC cells.
 16. The apparatus of claim 15, whereineach of the AMC metal layers is separated from all edges of themulti-layered PCB.
 17. The apparatus of claim 15, wherein each of theAMC metal layers has a square shape.
 18. The apparatus of claim 17,wherein each of the square shapes includes a metal divider that definesat least one inner rectangle.
 19. The apparatus of claim 18, wherein themetal divider defines at least two inner rectangles, each of the twoinner rectangles have a same set of dimensions, and the same set ofdimensions determines the frequency tuning and bandwidth of the AMCcells.
 20. The apparatus of claim 15, wherein at least one of the AMCmetal layers is configured to reflect energy radiated by at least one ofthe plurality of PIFAs to produce a directional radiation pattern.